The following descriptions for the abbreviations used in this specification apply:    Alt Alternative    DeNB Donor eNB    eNB enhanced Node B    E-UTRA Evolved Universal Terrestrial Radio Access    GW Gateway    HO Handover    IE Information Element    LTE Long Term Evolution    LTE-A LTE-Advanced    MBSFN Multi-Media Broadcast over a Single Frequency Network    MME Mobility Management Entity    MSE Mobility State Estimate    PGW Packet Data Network Gateway    RAT Radio Access Technology    Rel. Release    RLF Radio Link Failure    RN Relay Node    RRC Radio Resource Control    RSRP Reference Signal Received Power    SF Scaling Factor    SGW Serving Gateway    TTT Time-To-Trigger    Tx Transmission    UE User equipment
Embodiments of the present invention relate to LTE-Advanced, and in particular to relaying.
Relaying is considered for LTE-Advanced as a tool to improve, e.g. the coverage of high data rates, group mobility, temporary network deployment, the cell-edge throughput and/or to provide coverage in new areas. Relay as an important topic for Release (Rel.) 10 has been discussed in 3GPP. In a relay system, a relay node (RN) acts as UE from donor eNB (DeNB) point of view, while it behaves as an eNB for the UEs served by the RN. Therefore, the RN supports eNB functionality as well as UE functionality.
FIG. 2 shows a relay system architecture. It is noted that Alt1 to Alt3 show different alternatives of which elements are to be considered as part of the relay system. For example, Alt2 was selected by 3GPP for fixed relay implementation in Release 10.
Hitherto, only fixed relay for coverage extension scenario was discussed extensively in Rel.10. However, moving relays (relay nodes (RNs)), also referred to as mobile relays, are also of great interest, for example in high speed train infrastructure. Therefore, moving relay nodes, as an important candidate feature, are investigated in Rel. 11. In addition to the application area for the high speed trains, moving relay nodes can be also mounted on busses, trams, ferries, and any other kind of vehicles depending on the target service. An example high speed train scenario is illustrated in FIG. 3 where two moving RNs are mounted on train carriages. In this example, there is one moving relay mounted on each carriage. It is worth noting that the access link antennas of the moving relay node are installed inside the carriage and the backhaul link antennas are installed outside the carriage. Such a configuration prevents penetration loss.
Furthermore, there are three types of RNs standardized in LTE-Advanced Release 10. The functionalities defined for the fixed relays can also apply to moving relays. These types are briefly described in the following:                Type 1: This is an inband RN. Hence, to prevent self interference between backhaul and access links, a half-duplex operation is employed. During the backhaul subframes, the RN configures Multi-Media Broadcast over a Single Frequency Network (MBSFN) subframes on the access link in the downlink. The beginning of an MBSFN subframe contains cell-specific reference signals. Release 8 UEs receive these signals and ignore the rest of the MBSFN subframe.        Type 1a: This is an outband RN. That is, on backhaul and access links different frequency bands are utilized. As there is no self interference, there is no need for MBSFN subframes on the access link. All the subframes in an LTE frame are utilized both on the access and backhaul links.        Type 1b: This is an inband RN with sufficient isolation between backhaul and access links. Thanks to this sufficient isolation, all the subframes in an LTE frame can be utilized and there is no need for MBSFN subframes. Considering the penetration loss between inside and outside the carriage, a sufficient isolation is assumed in the moving relay scenario and hence Type 1b is viable.        
In the moving relay scenario, there might occur problems when performing a handover of a user equipment (relay-UE) from a moving relay node to fixed eNB or other fixed base station.